Assessment of optical phonons in BeTe, BexZn1-xTe, p-BeTe epilayers and BeTe/ZnTe/GaAs (001) superlattices

Abstract

Comprehensive simulations for the polarization-dependent far-infrared (FIR) reflectance and transmission spectra are reported to assess the longitudinal-optical (ωLO) and transverse-optical (ωTO) phonons in binary BeTe (ZnTe)/GaAs (001), ternary alloy BexZn1-xTe/GaAs (001) epilayers and BeTe/ZnTe/GaAs (001) superlattices. The Kramers–Krönig analyses are performed to achieve the optical constants of bulk materials for constructing their frequency dependent dielectric functions. Both s-[Ts(ω)/Rs(ω)] and p-[Tp(ω)/Rp(ω)] polarized spectral calculations are attained at an oblique incidence [i.e., Berreman effect (BE)] using a three-phase model in a multilayer optics approach. For perfect thin epilayers, the BE method has offered an unambiguous appraisal of ωLO and ωTO phonons in the p-polarized [Tp(ω)/Rp(ω)] FIR spectra; while in the p-doped BeTe epilayer, it justified the LO–plasmon (ω+LOPL) coupled modes to be longitudinal in character. Careful assessment of the ω+LOPL by FIR spectroscopy offers an alternative, elegant and effective method, complementary to Raman scattering spectroscopy for estimating the free-carrier charge density η in technologically important doped semiconductor epilayers.